Die for forming self-tapping fastener blank

ABSTRACT

A header die for forming a self-tapping fastener blank provides die forming zones within which the blank is formed, the blank therby defining an odd number of lobes along a cross section taken perpendicular to its axis of rotation. The lobes define a relatively high out-of-round cross section along a tapered thread-forming zone, and a relatively low out-of-round cross section along the main body taken in a direction toward the drive head. Between the main body and tapered thread-forming zone is located an additional thread forming zone having an axial length of approximately one thread pitch and a cross section that conforms to the high out-of-round of the tapered zone. The maximum diameter (at the lobes) of the additional thread-forming section approximately matches that of the full-diameter main body section. A lower-diameter stabilizing section can be provided ahead of the tapered zone, adjacent the tip of the fastener.

RELATED APPLICATION

This is a divisional of co-pending U.S. patent application Ser. No.09/236,815 filed Jan. 25, 1999.

FIELD OF THE INVENTION

This invention relates to threaded fasteners and more particularly toself-tapping fasteners that form internal threads using a roll-formingprocess.

BACKGROUND OF THE INVENTION

Self-tapping fasteners that form threads by deforming a thread patternwithin a pilot hole have become increasingly popular. There are manyadvantages to using a roll-forming thread, rather than amore-traditional thread-cutting design. A very successful style ofroll-forming thread is the multiple-lobed fastener shown, for example,in Phipard, U.S. Pat. Nos. 3,195,156 and 3,918,345, the contents ofwhich are incorporated herein by reference. This fastener is availablefrom a variety of sources carrying the trademark TRILOBULAR, inconnection with a three-lobe thread-forming blank design.

FIGS. 1-5 illustrate a conventional three-lobed thread-forming blank 10and resulting fastener (21) according to the prior art. In manufacturinga threaded fastener, a blank 10 is first provided with a head 12 asdetailed. The head, 12 in this example is a standard hex washer headdesign. However any head formation enabling the driving of the fastenerin a rotary fashion about a central axis 14 can be formed. The head isformed by striking the end of a straight blank "wire" segment usingheader punches that forcibly deform one end of a metallic wire made ofsteel or another hard metal. As will be described further a header diedeforms a specialized tapered thread-forming and stabilizing section onthe opposite end (the "tip") of the shaft. The wire, at the time of headand tip formation, typically already has a lobular cross-section 16 asrevealed in FIG. 3. Each lobe 18 is, in essence, an "out-of-round"formation. In other words, the lobes present an eccentric cross sectionwith respect to an otherwise round shape. In fact, formation of theblank, prior to heading involves the drawing of a round-cross-sectionwire through a lobed female die to create the illustrated out-of-roundon the main body of the blank (10). The headed blank 10 is passedbetween a pair of forming dies to form thereon a set of external threads22 detailed generally in FIG. 4. These threads exhibit the out-of-roundcharacteristics of the blank. In general, the external apices 24 of eachthread are located at an outer diameter greater than that of theoriginal blank, since material has been displaced from the threadtroughs 26 outwardly at predetermined locations to form each apex.

All threads have a characteristic pitch and diameter. Because of thelobulation of the threads, the radial offset from the axis 14 will varyabout the circumference. In general, standard thread diameters andpitches are provided to lobular fasteners, but the lobes tend to have aslightly larger diameter than a standard thread diameter. This enablesthe lobes to positively form corresponding internal threads as thefastener is driven into an appropriately-sized pilot hole into the shapeof conforming internal threads.

In other words, as the fastener 21 (FIGS. 4 and 5) is rotated clockwise,the lobes engage the inner wall of the pilot hole (not shown) and beginto displace material within the pilot hole. The threaded fastener 21 isprovided with a discrete stabilizing zone 30 having stabilizing threads32, and a thread-forming zone 33 with corresponding thread-formingthreads 34. The stabilizing zone 30, as detailed in FIGS. 1 and 2, has areduced diameter, enabling it to fit within an untapped pilot hole in arelatively perpendicular fashion. The thread-forming zone 33 has asloped/tapered shape with diameter that increases linearly between thestabilizing zone and the full-diameter main body 20. Note that thethread stabilizing zone 30 has a higher out-of-round than the main body20. This is clear from the end-on view of FIG. 2. The thread formingzone 33 also has a higher out-of-round than the full-diameter main body20. In one example, the out-of-round of the thread forming zonegradually tapers back from the highest out-of-round adjacent to thestabilizing zone toward the lower out-of-round that defines thefull-diameter main body 20. In another, usually preferred example, thethread forming zone can define an approximately constant-profile highout-of-round along its entire axial length, that transitions stepwise atthe main body into the characteristic lower out-of-round. In connectionwith either example, note the difference between the high out-of-roundat the stabilizing section end (FIG. 2) and at the main body crosssection (FIG. 3).

As a fastener is driven into an untapped pilot hole, the thread-formingthreads 34 encounter the sidewalls of the hole initially. These threadsexhibit an increasing outer diameter and higher out-of-round. As such,the lobes are able to gradually apply increasing thread-forming pressureto the pilot hole until each formed internal thread is contacted by thefirst full-diameter thread 40. This first full-diameter thread 40 hasthe out-of-round profile of the rest of the main body. It provides thefinal formation of each thread in the pilot hole to the desired shape.

In general, to form a thread properly requires several swaging "blows"from the underlying lobes of the fastener. This process is, in essence,similar to the formation of a shape in a ductile metal by a blacksmith'shammer. A sufficient number of forming threads is necessary to completethe process. To make the process go more quickly, a high out-of-round,which concentrates the force of the blows is desirable. Use of a highout-of-round within the main, full-diameter threads substantiallyreduces the amount of torque that must be applied to form threads.However, this lower torque comes at a price, since it results in lessdiametrical material remaining in contact with the internal thread onceit is formed. Hence, it is more likely that failure will occur in such afastener system such failure, in general, results from axial pull-outor, when thicker nut members are used, fracture. Also, since area variesby the square of the radius, the use of a higher out-of-round crosssection results in a significantly reduced cross sectional area, whichlowers the screw's failure limit. Hence, self-tapping screws typicallyuse an out-of-round dimension that is a compromise between the optimumvalue for thread forming efficiency and the optimum for resistance tofailure.

Previous attempts to balance a desire for higher out-of-round, versusfailure resistance is described in U.S. Pat. No. 4,040,328 toMuenchinger. This patent provides a tapered point zone on the fastenerwith stabilizing threads that have a higher out-of-round than thefastener body. However, the out-of-round of the stabilizing threads is,in fact, significantly greater than that of the full-forming thread.This is a less efficient structure, since the stabilizing andthread-forming threads are tasked with virtually all the forming work,while the first full-diameter thread has the lower out-of-round crosssection, which is inefficient for thread forming purposes.

It is therefore an object of this invention to provide a fastener blank,and under-lying threaded fastener formed therefrom, that exhibitsreasonable low thread-forming torque, while maintaining good resistanceto failure, once it is in engagement within a nut-member or otherthread-formed hole.

SUMMARY OF THE INVENTION

This invention overcomes the disadvantages of the prior art by providinga header die for forming a blank, and corresponding fastener, with across section that defines a series of lobes, and that has an additionalthread-forming section between the lobed tapered thread-forming sectionand the full-diameter lobed main body of the blank. This additionalthread forming section is also substantially full-diameter and exhibitscross sectional lobes with a higher out-of-round than those of the mainbody blank/threads. The additional thread-forming section has an axiallength of approximately one thread pitch, thereby providing oneadditional high-out-of-round full-diameter thread forward of (in ahead-to-tip direction) the main body threads. The lobes of theadditional thread-forming thread are located at the full diameter, likethe adjacent main body threads, but have a higher contact pressure dueto less material in contact with the internal threads being formed. Assuch the additional full-diameter thread-forming thread applies morethread-forming pressure than would be applied by a conventional mainbody thread at the same axial position.

In an alternate embodiment, the blank can include the above-describedhigher out-of-round section on a blank that includes a tapered section,but no substantial stabilizing section forward thereof In each of theabove embodiments, the additional thread-forming section has anout-of-round defined by the out-of-round factor K (further definedhereinbelow) equal to approximately 0.2-0.3 times the relative threadpitch while the out-of-round of the main body threads is maintained at afactor K approximately 0.05-0.15 times the relative pitch.

A blank having the above-described thread forming and main body sectionscan be formed to selectively include either a stabilizing section or atip that begins at the tapered section by providing the header die witha knock-out pin in which the knock-out pin can be positioned to occupyor reveal part of a forming die cavity therein that conforms to the sizeand shape of the stabilizing section.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other objects and advantages of the invention willbecome more clear with reference to the following detailed descriptionas illustrated by the drawings in which:

FIG. 1, already described, is a side view of a self-tapping roll-formingfastener blank according to the prior art;

FIG. 2, already described, is a front-end view of the fastener of FIG.1;

FIG. 3, already described, is a cross-section of the fastener blanktaken along line 3--3 of FIG. 1;

FIG. 4, already described, is a broken side view of an exemplary threadpattern formed from the blank of FIG. 1;

FIG. 5, already described, is a more detailed view of the stabilizingand thread-forming sections of the fastener of FIG. 4;

FIG. 6 is a side view of a self-tapping roll-forming fastener blankaccording to this invention;

FIG. 7 is a side view of an exemplary thread pattern formed on thefastener blank of FIG. 6;

FIG. 8 is a side view of a self-tapping roll-forming fastener blankaccording to an alternate embodiment of this invention;

FIG. 9 is a side view of an exemplary thread pattern formed on the blankof FIG. 8;

FIG. 10 is a cross section of a typical fastener blank, illustrating asystem for measuring out-of-round;

FIG. 11 is a cross section of a header die arrangement for producing ablank according to one embodiment of this invention; and

FIG. 12 is a cross section of the header die arrangement of FIG. 11 forproducing a blank according to an alternate embodiment of the invention.

DETAILED DESCRIPTION

FIG. 6 illustrates a fastener blank according to a preferred embodimentof this invention. The blank 100 includes a drive head 102 having anydesired shape. As described above, the head has been formed on the blankusing header punches or another acceptable method. The blank 100 isformed from a hardenable metal such as low-medium carbon steel. Finalhardening is typically accomplished in the form of heat treating, casehardening, magnetic induction hardening, nitride coating and the likeafter final thread formation on the blank has occurred.

The blank in this embodiment includes three discrete lobes like thoseshown with reference to FIGS. 1-5. In general, more lobes can be used.It has been found, however, that three lobes are acceptable. When morelobes are used, it is preferable that an odd number of lobes be present.

The blank 100 includes a main body 104, a stabilizing section 106, atapered thread-forming section 108 and a unique additionalthread-forming section 110. The length of each section, 104, 106, 108and 110 (LM, LS, LT and LA, respectively) of the blank is herein definedin terms of the number of standard pitch lengths that can be applied tothe respective fastener blank section as it is formed.

By way of background, a lobular fastener can be formed in accordancewith the teachings of Phipard, Jr., U.S. Pat. No. 3,918,345,incorporated herein by reference (see, for example, FIG. 5 therein)using a pair of forming dies that are moved in predetermined oppositedirections in which a headed blank is passed therebetween. The formingdies include linear grooves that conform to thread shapes and are set atan appropriate pitch spacing from each other. Typically, the formingdies define curved or angled/inclined surfaces that taper toward eachother near the tip of the blank (opposite the head), conforming with thetapered thread-forming and stabilizing zone of the associated blank.During formation, the dies are first brought into compressive,permanently deforming contact with the blank, one die contacting a lobe,and the other contacting an opposing valley on the three-lobe,three-valley blank. The threads are pressed into the contact points atthis time. As a moving die passes by a stationary die, the blank isrotated between them with its center axis 112 defining an oscillatingpath. This oscillation corresponds to the rotation of the blank aboutits lobes. The dies maintain a constant spacing as they move, forming athread pattern of predetermined depth (based upon the degree of dieseparation) on the blank surface. Note that, during fastenermanufacture, a slight degree of thread underfill/overfill may existgiven the symmetrical spacing of the dies. This underfill/overfill,which occurs primarily in the stabilizing and thread forming sections ofthe fastener, does not appreciably affect the performance of thefastener.

The finished fastener which is shown in FIG. 7 including threads willinclude a set of main body threads 120 that are substantially even inpitch and diameter. The stabilizing threads 122, which are typically11/2-3 pitches in length (length LS), are smaller in diameter. Thethread-forming threads 124, 126 and 128, shown here as three distinctthreads that each increase in diameter in conformance with theincreasing in diameter of the taper from the front end 130 of thefastener to the head 102. Typically, two-three forming threads areprovided in this embodiment (length LT). In an alternate embodiment,three-four forming threads (or more) are provided. As noted above, thestabilizing and thread-forming blank sections 106 and 108, respectively,and the corresponding threads 122, 124, 126 and 128 define andout-of-round that is greater than that of the main body 104 and itsthreads 120. This is, as noted above, desired to reduce thethread-forming torque required when the fastener is driven into anunthreaded pilot hole. With reference again to Phipard, Jr. '345, atechnique for defining out-of-round in a multi-lobe fastener blank isdescribed. This measurement technique is detailed generally in FIG. 10.The cross-sectional outline 150 of the blank corresponds to anodd-numbered polygon. In this case it is a triangle. The triangle iscircumscribed about the central axis 112. The individual curved segmentsthat make up the outline 150 are particularly defined according to knownconventions described, for example, in the Phipard patents noted above.Definitions of the outline shape are also available in a variety ofliterature related to TRILOBULAR™ fasteners available from ResearchEngineering and Manufacturing, Inc. of Middletown, R.I. A circle 152 isshown circumscribing each apex or corner 154 of the outline 150. This isa circle of maximum diameter for the blank. It is centered about theaxis 112. Another circle 156, also centered about the axis 112 contactsthe most inwardly located valley 158 of the outline 150 with respect tothe axis 112. The diameter of the outer circle 152 is denoted as C. Thedistance between an apex 154 and an opposing valley 158 is denoted as D.The difference between C and D is denoted as the dimension value K. Kis, in essence, the magnitude of the out-of-round inherent in a givenblank cross section.

Referring again to FIGS. 6 and 7 the main body is provided with adimension K that is relatively low, being 0.05-0.15 times the relativethread pitch P conversely, the out-of-round of the thread-formingsection 108, and associated threads 124, 126 and 128 is defined by a Kapproximately 0.20-0.30 times the thread pitch P. According to thisembodiment, the additional thread-forming section 110, which has anaxial length LA of approximately one pitch length (P) maintains theout-of-round dimension of the adjacent portion 160 of the taperedthread-forming section 108. In other words, a thread 162 is defined onthe section 110 that has a relatively high out-of-round or K equal to0.20-0.30 times the pitch P of the fastener thread. It is expresslycontemplated, however that, the section 110 can have an axial lengthsufficient to accommodate two or more full-diameter thread-formingthreads thereon, according to an alternate embodiment of this invention.The diameter of the lobes of this thread are substantially the same asthose of the adjacent main body threads. Hence the zone 110 presents afull-diameter forming profile to the internal threads, but does so at ahigher pressure, since less area on each lobe of the thread 162 inadditional zone 110 is in contact with the internal thread. Of coursethere may be slight variations in diameter between the thread 162 andthe main body threads 120, but the thread is sufficiently close indiameter to be termed a full-diameter thread with respect to the fulldiameter main body threads 120. The next adjacent thread 170 among themain body threads 120 drops in out-of-round abruptly to have a K equalto 0.05-0.15 in this embodiment. By providing an additional thread 162having the above-described high out-of-round, with an outer diameterthat is essentially the same as the remainder of the main body threads120, the torque necessary to form a thread in a pilot hole issubstantially reduced. Rather than having the thread-forming zonetransition immediately into a low out-of-round main body zone, thethread 162 acts as a full diameter transition thread that stillmaintains a high contact pressure for final formation of threads at fulldiameter. Hence, when the main body threads 120 finally reach the newlyformed internal threads of the pilot hole, they should not be requiredto exert substantial formation pressure themselves.

Reference is now made to FIGS. 8 and 9 which show a fastener blank andresulting threaded fastener according to alternate embodiment. Unlikethe embodiment shown in FIGS. 6 and 7, the embodiment detailed in FIGS.8 and 9 does not include a stabilizing section. In some applications, astabilizing section is not necessary or desired. FIG. 8, particularly,shows a fastener blank 200 having a formed head 202 thereon of anappropriate shape and size. The blank includes a main body 204 having alength L1M also detailed is a tapered thread-forming section 206 havinga length L1T and an additional section 208 disposed axially between thetapered thread-forming section 206 and main body section 204. Theadditional section has a length L1A. A relatively small tip portion 210(usually 0.010-0.015 inch in axial length) is also depicted. This isexcess material displaced during the tip formation process in the headerdie and is not significant to the structure defined herein as describedabove. In particular, the tip often serves as a witness mark thatindicates whether the full section of the header die has been filled outduring blank manufacture. The axial length of the main body 204 variesdepending upon the desired length of the fastener. As shown in FIG. 9, aseries of main body threads 220 are defined on the main body using thethread die-forming process described above. The out-of-round K for thesethreads is approximately 0.05-0.15 times the pitch P1. Threediametrically increasing thread-forming threads 224, 226 and 228 arealso formed. Their out-of-round, as defined above, is a K equal to0.20-0.30 times P1. The length L1T of the tapered thread-forming sectionis sufficient to provide approximately three threads thereon. Finally,the additional thread-forming thread 230 formed on the additionalsection 208 has the high out-of-round K equal to 0.20-0.30 times P1, andprovides the full-diameter thread-forming transition into the main bodythreads. The additional section length L1A, is, of course, sufficient toprovide one thread pitch at minimum.

The formation of a finished blank (100) detailed in FIGS. 5 and 6 can beaccomplished according to FIG. 11. A hard header die 300 is shown. Itdefines a forming die cavity 302, into which a cut-off piece of wire orrod 304 of predetermined size is placed. The die cavity 302 is adimensioned hole that conforms to the desired finished blank shape. Thedie cavity 302 has sidewalls of sufficient thickness and hardness toensure that no deformation of the die cavity 302 will occur as a pieceof wire or rod is driven thereinto to be plastically deformed into theblank shape. The cross section of the die cavity 302 (not shown), ofcourse, defines three or more lobes as described above. The wire or rodsection used to form the blank can also include three or more conforminglobes. The wire or rod typically has a cross section that conforms tothe desired main body shape so further forming of this main body portionof the blank is minimal. In general, the die 300 is formed according toconventional techniques, using known materials and dimensional sizingfor sidewall thickness, etc.

Formation of a finished fastener blank often occurs in several strikesapplied by a ram or punches 305 (shown in phantom). The punches aretypically driven by a powerful mechanical actuator (not shown) thatstrikes the blank under great pressure (see arrow 307) to cause both theblank head and internal blank shape to be formed simultaneously. Severaldifferently shaped punches and/or header dies can be used duringformation of the blank and blank head, each with a shape that conformsprogressively more closely to that of the finished blank drive head 102.In this example, that drive head 102 defines a conventional hex washerhead shape as shown above. The punches used herein are consideredconventional.

The die cavity 302 defines the distinct shapes of the blank sectionsaccording to each of the embodiments of this invention. The die cavity302 defines a series of shaped sections that form the respectivesections of the finished fastener blank through plastic deformation asthe initial rod or wire is driven into the die cavity by the punch 305.The sections each define a multi-lobed cross section having the desiredout-of-round configuration as discussed above. The die cavity sectionsinclude an elongated main body die cavity section 306 for enclosing theblank's corresponding main body adjacent the opening of the die cavity.The neighboring full-diameter, high out-of-round thread forming section312 having a high out-of round is located inwardly of the main body diecavity section 306. Likewise, the tapered thread forming die cavitysection 312 and stabilizing section die cavity section 316 are eachlocated further inwardly, respectively. During the forming process, therod or wire is seated inwardly as far as it can go. It typically seatsonto the front of the full-diameter thread forming section 312. Eachstrike of the punch or punches, causes the rod or wire tip to deforminto the next forward section as it is driven further into the diecavity. The knock-out pin acts as a stop to prevent further inwardmovement of the blank into the die cavity 302. This pin is formed from ahardened material according to known processes. It can move axiallyinwardly and outwardly (double arrow 348) under the force of amechanical actuator (not shown) of known design. The pin mechanism canbe locked into position (not shown) so as to maintain its positionfirmly when it is acting as a stop as shown in FIGS. 11 and 12. When theblank is to be removed from the die cavity 302, the knock out pin ismoved toward the cavity front opening a sufficient distance to eject theblank. The blank can then be transferred by know techniques to anothercavity for further forming or to a threading mechanism or machine forforming of the threads.

FIG. 12 details the die 300 configured to form a blank (200) accordingto the embodiment detailed in FIGS. 8 and 9. This blank is substantiallysimilar in size and shape to the blank (100) described above. However,it omits a stabilizing section at its front. As described above, theknock-out pin can be selectively moved (double arrow 348) toward andaway from the front opening of the die cavity 302. Hence, the knock outpin can be moved by its actuator to selectively occupy the area of thestabilization section die cavity 316. The pin 330 typically has a crosssection that matches that of this section. This when it moves toward thecavity front opening its is not blocked by the larger diameter sections300, 312 and 314. To create a blank 100 according to FIGS. 6, 7 and 11,the knock-out pin is positioned approximately 11/2-3 pitch lengthsforwardly of the tapered thread forming section 314. This allows thefront tip of the rod or wire 340 to be driven fully into the stabilizingdie cavity section 316. Conversely, when the section 316 is occupied bythe knock-out pin 330, its front face 320 provides a stop that preventsthe stabilizing section from being formed, creating the alternatefinished blank (200). The knock-out pin 330 can be moved to each ofthese alternate positions (FIG. 11 or FIG. 12). Appropriate lockingmechanisms can be provided to secure the pin 330 in either of the stoppositions described above.

The foregoing has been a detailed description of preferred embodimentsof the invention. Various modifications and additions can be madewithout departing from the spirit and scope of this invention. Forexample, the blank can include further forming and stabilizing sections,in addition to the full-diameter forming section detailed herein. Avariety of other forming techniques can be used to form blanks, driveheads and thread patterns including fully enveloping dies, cutting toolsor rolling dies. Finally, the thread profile depicted herein is of aconventional triangular/straight-line configuration. It is expresslycontemplated that a blank according to this invention can be providedwith any kind of thread profile including a curved/radius profile, acupped profile or a square/Acme profile. In addition, while a range of Kfactors for out-of-round are specified hereinabove for various blanksections, it is expressly contemplated that these values can be variedfor applications having particular size, shape and materialrequirements. The exact K factor can be determined for such anapplication using empirical data based upon physical tests andexperiments on fasteners formed with a given set of properties.Accordingly, this description is meant to be taken only by way ofexample, and not to otherwise limit the scope of the invention.

What is claimed is:
 1. A header die for forming a threaded fastenerblank comprising:a forming die cavity for receiving a substantiallylinear blank having a cross section, taken through an axis, that definesat least three lobes and three valleys therebetween, the die cavityincluding walls for forming (1) a main body section extending in anaxial direction from a drive head toward a tip, the main body sectionhaving main body valleys with a main body valley maximum diameter andmain body lobes with a main body lobe maximum diameter and definingtherebetween a main body section out-of-round dimension, (2) a taperedthread-forming section located forward, taken in the axial directiontoward the tip, of the main body section, the tapered thread-formingsection having, at each axial point therealong, tapered thread-formingsection valleys with a tapered thread-forming valley maximum diameterand tapered thread-forming valley lobes with a tapered thread-forminglobe maximum diameter and defining therebetween a tapered thread-formingsection out-of-round dimension, the main body section out-of rounddimension being lower than the tapered thread-forming sectionout-of-round dimension, and (3) a full-diameter thread-forming sectionlocated axially between the main body section and the taperedthread-forming section, the full diameter thread forming section havingfull-diameter thread-forming section valleys with a full-diameterthread-forming valley maximum diameter and full-diameter thread-formingvalley lobes with a full-diameter thread-forming lobe maximum diameterand defining therebetween a full-diameter thread-forming sectionout-of-round dimension, wherein the full-diameter thread-forming lobemaximum diameter is approximately equal to the main body lobe maximumdiameter and the full-diameter thread-forming out-of-round dimension ishigher than the main body out-of-round dimension; and a selectivelypositionable knock-out pin that stops linear movement of the blankbeyond a predetermined axial point during formation, the knock-out pinbeing constructed and arranged to selectively uncover and reveal astabilizing section forming die cavity axially forward of a part of thedie cavity that forms the tapered thread-forming section, thestabilizing section forming die cavity being constructed and arranged toform a blank stabilizing section with a lower stabilizing lobe maximumdiameter than the main body lobe maximum diameter.
 2. The header die asset forth in claim 1 wherein the knock-out pin is movable axially adistance equal to a distance covered by at least 11/2 thread pitches ofpredetermined size arranged to be located on the blank.
 3. The headerdie as set forth in claim 2 wherein the forming die cavity includes apart for forming the full-diameter thread-forming section having anaxial distance equal to at least one thread pitch of the predeterminedsize.
 4. The header die as set forth in claim 2 wherein the blank isconstructed and arranged to receive threads having a pitch P and whereinthe out-of-round of the full-diameter thread forming section is definedby a factor K approximately equal to 0.20-0.30 times P, based upon adifference between a radial length of thread forming section valleys andthread forming section lobes, with respect to an axis of the blank.